1. Field of the Invention
The present invention relates generally to the field of technology involving compositions that are useful for producing shaped bodies through a variety of forming techniques. More particularly, the invention is specifically directed to an improved composition of this type wherein metal compounds are utilized to form shaped bodies which may be reduced and sintered to produce metal articles.
2. Description of the Prior Art
The prior art has recognized that metallic shapes such as filaments and fibers may be made by wetting fine particles of metallic compounds with a binding agent, forming a green body from this mixture by molding, extruding or the like, and thereafter reducing the metallic compound to its free metal form and sintering the metal particles to produce a dense metal product. This basic technique has proved quite economical in both operational and material costs due to the fact that expensive and heavy equipment for metal shaping is no longer necessary and waste is minimized since materials can be recycled. Moreover, the final products only require minimum working or finishing treatments.
An example of such known technology is the McIntire et al U.S. Pat. No. 3,671,228 which discloses that high density metallic bodies may be made from reducible metal compounds by forming agglomerates thereof through mixing fine particles of the compounds with a plasticizer or binder. The agglomerates are then compacted into the desired shapes, such as by extrusion to form filamentary articles, and thereafter subjecting the shaped bodies to a reducing environment. The resulting free metal body is then sintered into a very high density metal product. By mixing metallic compounds of different metals in forming the compacted agglomerates, it is possible to produce sintered alloy products for various applications. This patent recognizes that the type of binder or plasticizer utilized to form its agglomerates does affect the green strength of the compacted shapes and surface conditions of the sintered products. However, this technique is primarily concerned with forming an agglomerate that is essentially in the form of a paste mix having a high degree of viscosity so that self-supporting compacted shapes may be made therefrom through extrusion or die-forming.
Another known technique for shaping metallic compound compositions to form free metal articles through subsequent reduction and sintering involves the procedure of slip casting. In this technique, a fine particulate metallic compound that is capable of being reduced to the metallic state is dispersed in a carrier liquid to form a slurry. The viscosity of the slurry is necessarily extremely low so that it may be poured into a mold constructed of a substance that is capable of absorbing the carrier liquid. The mold draws off the carrier liquid, thereby leaving the particulate material deposited on the inner walls of the mold in the desired shape. The formed shape is then subjected to partial or complete drying which causes the shape to shrink a sufficient amount so that it may be easily removed from the mold. This slipcast article, comprising essentially compacted metallic compound particles, is then placed into a reducing environment to convert the compound into free metal. Final sintering of the resulting metallic article produces a dense metal product, with the final density being generally dependent upon the particle size of the precursor metallic compound. Prior art examples of slip casting are disclosed by the Stoddard et al U.S. Pat. No. 3,052,532 and Sagmuller et al U.S. Pat. No. 3,672,882.
In addition to the above described compositions and forming techniques, other similar systems are known in the prior art wherein shaped bodies are formed by mixing particulate metallic and refractory compounds with some form of binder agent so that the resulting agglomerate may be compacted into a desired shape and subjected to heat treatments. Variations of this basic concept have depended primarily upon the type of binder or suspension medium and the specific compacting or forming technique being utilized.
The physical characteristics of a given agglomerate have been found to be directly related to the particle size of the precursor material and the nature of the binding or suspension medium. For certain molding techniques, such as extrusion or ore compaction, it is highly desirable to provide a very viscous agglomerate mix that is substantially self-supporting in nature. Spin casting of the mix into filamentary shapes requires mixes of intermediate viscosities, while slip casting is advantageously conducted with extremely low viscosity or liquid-like agglomerates. As such, known agglomerate mix compositions are basically not versatile in that a given composition possessing specific rheological characteristics is generally restricted to a particular optimum forming technique.